Synthesis of PdII Complexes Bearing pNHC Ligands by Oxidative Addition of 8-Halogenotheophyllines and 8-Bromoadenine to Pd0

Synthesis, Base Pairing Properties, and Biological Activity Studies of Platinum(II) Complexes Based on Uracil Nucleosides

The synthesis and base pairing properties of platinum complexes based on uridine and deoxyuridine nucleosides and preliminary studies of their antiproliferative activity are described. Platinum(II) uridine and deoxyuridine complexes were synthesized by C-I oxidative addition to Pt(0)(PPh3)4. First, the synthesis was performed with protected nucleosides to generate complexes 1 and 2, which were deprotected under basic conditions, affording complexes 3 and 4 in good yields. The synthesis with the unprotected nucleosides was also performed and provided complexes 3 and 4 effectively. Base pairing interactions were measured for complex 1, either for self-base pairing or for the Watson-Crick base pair. Complex 1 undergoes self-base pairing in CDCl3, and this aggregation was found not to be dependent on metalation. Contrastingly, for the Watson-Crick base pair with adenine, base pairing was also observed, but metalation was found to affect hydrogen bonding considerably. Complexes 3 and 4 and the corresponding ligand precursors were evaluated for their antiproliferative activity against human glioblastoma cell line U-251. The compounds showed IC50 values of 3.30 (3) and 1.84 (4) μM but are also toxic for nontumorous cell lines.

Metal complexes of xanthine and its derivatives: Synthesis and biological activity

Xanthine and its derivatives are considered an important class of N-heterocyclic purine compounds that have gained significant importance in medicinal chemistry. N-heterocyclic carbene (NHC) and N-coordinated metal complexes of xanthine and its derivatives have revealed a range of new possibilities for their use as therapeutic agents in addition to their established catalytic behavior. The metal complexes of xanthine and its derivatives have been designed and synthesized for the exploration of their potential therapeutic applications. These metal complexes based on the xanthine scaffold exhibited various potential medicinal applications including anticancer, antibacterial, and antileishmanial activity. The metal complexes of xanthine and its derivatives shall pave the way for the rational design and development of new therapeutic agents. In the present comprehensive review, we highlighted the recent advancements in the synthesis and medicinal applications of metal complexes based on N-heterocyclic carbene (NHC) derived from xanthine scaffolds.

Oxidative addition of a 8-bromotheobromine derivative to d 10 metals

Reaction of 8-bromo-7-ethyl-3-methylxanthine 1 with zerovalent group 10 metal complexes gave via an oxidative addition of the C–Br bond the neutral complexes trans-[2] (M = Pd) and trans-[3] (M = Pt) bearing a theobromine-derived azolato ligand. While the oxidative addition to [Pd0(PPh3)4] gave exclusively trans-[2], the reaction with the more substitution-inert [Pt0(PPh3)4] yielded after 1 day the kinetic product cis-[3], which was converted under heating for a total of 3 days completely into the thermodynamically more stable complex trans-[3]. Treatment of trans-[2], trans-[3] or the mixture of cis-/trans-[3] with the proton source HBF4⋅Et2O led to complexes trans-[4]BF4, trans-[5]BF4 and a mixture of cis/trans-[5]BF4 with retention of the original ratio of cis to trans, respectively. The molecular structures of the azolato complexes trans-[2] and trans-[3] and of the theobromine derived pNHC complexes trans-[4]BF4 and trans-[5]BF4 have been determined by X-ray diffraction studies.

Mononuclear and dinuclear gold(i) complexes with a caffeine-based di(N-heterocyclic carbene) ligand: synthesis, reactivity and structural DFT analysis

Two gold(i) complexes with caffeine-based di(N-heterocyclic carbene) ligands were synthesised and fully characterised.

Chemoselective synthesis of heterobimetallic bis-NHC complexes

Bis-NHC precursors composed of an azolium and a 2-halogenoazole group connected by different linkers have been site-selectively metallated to give heterobimetallic complexes from a single-frame bis-NHC ligand. The azolium group reacts with a base and oxidized metal centers to give NHC complexes with no participation of the halogenoazole, while the halogenoazole reacts in an oxidative addition with low-valent transition metals to give azolato complexes with no participation of the azolium group.

Synthesis of IrIII Hydrido Complexes by Oxidative Addition of Halogenated Theophylline and Adenine Derivatives

The Ir^III hydrido complexes [1] and [2] have been synthesized by the regioselective oxidative addition of the N7-H bond of 8-halogenotheophyllines to [IrCl(coe)₂]₂ in the presence of PPh₃. The use of dppf in this reaction yielded the bimetallic Ir^III/Fe^II hydrido complexes [3] and [4]. X-ray diffraction studies confirmed that complexes [1]-[4] feature a theophyllinato ligand coordinated to the metal center in the rarely observed, chelating fashion via the N7 and O1 atoms. In addition, 8-bromoadenine reacts with [IrCl(coe)₂]₂ in the presence of PPh₃ to form the Ir^III hydrido complex [5] which features one anionic 8-bromoadeninato and one neutral 8-bromoadenine ligand linked by an intramolecular hydrogen bond. Complex [5] was characterized by high-resolution mass spectrometry and an X-ray diffraction analysis but could not be analyzed by nuclear magnetic resonance spectroscopy because of its low solubility.